allure report installed but not findable

Solution 1:

Download and install the latest Allure version as .tgz archive.

curl -o allure-2.6.0.tgz -Ls https://dl.bintray.com/qameta/generic/io/qameta/allure/allure/2.6.0/allure-2.6.0.tgz   
sudo tar -zxvf allure-2.6.0.tgz -C /opt/   
sudo ln -s /opt/allure-2.6.0/bin/allure /usr/bin/allure  
allure --version 

You mentioned in the question that you are using an Ubuntu 18.04 Docker image, but there is also a dedicated Allure Docker Service image.

This docker container allows you to see up-to-date reports simply mounting your allure-results directory in the container. Every time new results appear (generated for your tests), Allure Docker Service will detect those changes and it will generate a new report automatically (optional: send results / generate reports through the API), which you will see by refreshing your web browser.